To detect each of the plurality of divided rib areas by separating respective rib areas connected by calcification or the like.

In the method of detecting the rib area by labeling each rib area of a subject from a three-dimensional image indicating the subject, whether or not it is an area detected as one rib area by the connection of the plurality of rib areas is decided on the basis of the shape information of each detected rib area. When it is decided that it is the area detected as one rib area by the connection of the plurality of rib areas, the detected rib area is divided into the plurality of rib areas configuring one rib area, and when the division into the plurality of rib areas is made, by labeling the plurality of divided rib areas respectively, the rib area is detected again.